In recent years, display apparatuses using organic electroluminescence devices (so-called organic EL devices) have been drawing attention as flat panel type display apparatuses which are light in weight and high in efficiency.
The organic electroluminescence devices for constituting a display apparatus as above-mentioned are provided on a transparent substrate formed, for example, of a glass or the like, and each have an anode formed of ITO (Indium Tin Oxide), an organic layer, and a cathode stacked in this order from the substrate side. The organic layer has a configuration in which a hole injection layer, a hole transport layer and an electron transporting light emitting layer are sequentially stacked in this order from the anode side. In the organic electroluminescence device thus configured, electrons injected from the cathode and holes injected from the anode are recombined in the light emitting layer, and light generated upon the recombination is taken out from the substrate side through the anode.
Organic electroluminescence devices include, other than that configured as above, a so-called top emission type one in which a cathode, an organic layer, and an anode are sequentially stacked in this order from the side of a substrate, and, further, the electrode located on the upper side (the upper electrode as cathode or anode) is formed of a transparent material, whereby light is taken out from the side of the upper electrode opposite to the substrate. Particularly, in an active matrix type display apparatus having thin film transistors (TFTs) provided on a substrate, adoption of a so-called top emission structure, in which top emission type organic electroluminescence devices are provided over the substrate formed with the TFTs, is advantageous in enhancing the aperture ratio of light emitting portions.
Meanwhile, in the case where putting an organic EL display to practical use is considered, it is necessary, other than enhancement of light emission by broadening the aperture of the organic electroluminescence device, to enhance the luminous efficiency of the organic electroluminescence device. In view of this, various materials and layer configurations have been investigated for enhancing the luminous efficiency.
For instance, in regard of a red light emitting device, a configuration in which a naphthacene derivative (inclusive of rubrene derivatives) is used as a dopant material has been proposed as a new red light emitting material substituting for the pyran derivatives represented by DCJTB which have hitherto been known (see, for example, Patent Documents 1 and 2 set forth below).
Besides, also disposed in Patent Document 2 is a configuration in which white light emission is achieved by stacking a second light emitting layer containing a penillene derivative and an anthracene derivative, on a first light emitting layer using a rubrene derivative as a dopant material.
Furthermore, a configuration is proposed in which white light emission is achieved by a method in which an electron transport layer or a hole transport layer, which is adjacent to a blue light emitting layer, is doped with a rubrene derivative (see Patent Document 3 set forth below).